﻿272 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  11 
  

  

  been 
  the 
  effect 
  of 
  diffraction 
  of 
  the 
  light 
  f 
  ocussed 
  in 
  the 
  plane 
  of 
  the 
  filament, 
  

   by 
  the 
  filament. 
  

  

  A 
  rigorous 
  solution 
  of 
  the 
  problem 
  of 
  diffraction 
  by 
  an 
  obstacle 
  in 
  the 
  focal 
  

   plane 
  has 
  not 
  been 
  attempted. 
  It 
  can 
  be 
  shown 
  by 
  deduction 
  that 
  only 
  the 
  

   light 
  diffracted 
  by 
  the 
  objective 
  aperture 
  is 
  again 
  diffracted 
  by 
  the 
  filament; 
  

   while 
  the 
  undiflfracted 
  portion 
  of 
  the 
  converging 
  beam 
  passes 
  the 
  filament 
  un- 
  

   disturbed. 
  To 
  avoid 
  a 
  visible 
  effect 
  of 
  diffraction 
  the 
  filament 
  and 
  image 
  

   are 
  viewed 
  through 
  an 
  aperture 
  smaller 
  than 
  the 
  objective 
  in 
  angular 
  meas- 
  

   ure. 
  The 
  actual 
  values 
  of 
  the 
  entrance 
  and 
  exit 
  apertures 
  of 
  the 
  telescope 
  

   depend 
  on 
  various 
  factors. 
  Large 
  entrance 
  apertures 
  must 
  be 
  used. 
  

  

  As 
  a 
  result 
  of 
  improvements 
  in 
  the 
  design 
  of 
  this 
  optical 
  pyrometer, 
  the 
  

   precision 
  attainable 
  has 
  been 
  markedly 
  increased, 
  now 
  surpassing, 
  probably, 
  

   that 
  of 
  the 
  contrast 
  photometer. 
  High 
  temperatures 
  are 
  easily 
  estimated 
  

   to 
  fractions 
  of 
  a 
  degree, 
  far 
  within 
  the 
  limits 
  of 
  certainty 
  of 
  the 
  so-called 
  

   high 
  temperature 
  scale. 
  The 
  disadvantage 
  lying 
  in 
  the 
  use 
  of 
  the 
  optical 
  

   scale 
  founded 
  on 
  the 
  Wien-Planck 
  laws, 
  instead 
  of 
  the 
  radiation 
  scale 
  of 
  

   Stefan-Boltzman 
  laws, 
  is 
  balanced 
  by 
  the 
  extreme 
  ease 
  of 
  manipulation 
  

   and 
  high 
  precision 
  attainable. 
  However, 
  the 
  lack 
  of 
  agreement 
  between 
  

   the 
  different 
  scales 
  of 
  temperature 
  is 
  at 
  present 
  not 
  great, 
  nor 
  serious, 
  and 
  has 
  

   been 
  found 
  negligible 
  for 
  most 
  purposes. 
  

  

  A 
  form 
  of 
  micropyrometer 
  has 
  been 
  devised 
  for 
  measuring 
  the 
  temperature 
  

   of 
  a 
  microscopic 
  or 
  very 
  small 
  object 
  with 
  the 
  same 
  precision 
  as 
  with 
  large 
  

   objects. 
  For 
  example 
  a 
  small 
  lamp 
  filament 
  or 
  a 
  minute 
  black-body 
  fur- 
  

   nace 
  can 
  be 
  examined. 
  

  

  The 
  writers 
  believe 
  that 
  significant 
  progress 
  has 
  been 
  made 
  toward 
  placing 
  

   this 
  form 
  of 
  optical 
  pyrometer 
  in 
  sound 
  relation 
  with 
  the 
  laws 
  of 
  geometrical 
  

   and 
  physical 
  optics, 
  and 
  in 
  developing 
  an 
  instrument 
  of 
  precision. 
  

  

  S. 
  P. 
  Fergusson 
  : 
  Equipment 
  for 
  aerological 
  kite-Hying 
  at 
  the 
  greatest 
  possible 
  

   heights 
  (illustrated). 
  It 
  was 
  discussed 
  by 
  Messrs. 
  L. 
  H. 
  Adams, 
  Crittenden, 
  

   Humphreys 
  and 
  Tuckerman. 
  

  

  (Author's 
  abstract.) 
  With 
  kites 
  and 
  accessories 
  in 
  use 
  at 
  the 
  present 
  time 
  

   the 
  average 
  heights 
  attained 
  are 
  about 
  3500 
  meters 
  and 
  the 
  maximum 
  about 
  

   7000. 
  From 
  an 
  experimental 
  study 
  of 
  materials, 
  forms 
  of 
  kites, 
  methods 
  of 
  

   construction, 
  lines, 
  etc., 
  the 
  author 
  has 
  found 
  that 
  these 
  heights 
  can 
  be 
  in- 
  

   creased 
  considerably 
  if 
  the 
  largest 
  kites 
  and 
  the 
  largest 
  sizes 
  of 
  wire 
  for 
  lines 
  

   are 
  used. 
  Large 
  kites 
  are 
  more 
  economical 
  and 
  are 
  so 
  much 
  stronger 
  than 
  

   smaller 
  ones 
  of 
  nearly 
  the 
  same 
  specific 
  weight 
  that 
  there 
  is 
  no 
  danger 
  of 
  

   wrecking 
  a 
  kite 
  in 
  the 
  strongest 
  wind 
  likely 
  to 
  be 
  encountered 
  aloft; 
  also 
  

   they 
  are 
  steadier 
  and 
  more 
  stable 
  and 
  since 
  their 
  specific 
  weight 
  when 
  car- 
  

   rying 
  the 
  usual 
  recording 
  instruments 
  is 
  smaller, 
  ascensions 
  are 
  possible 
  

   through 
  a 
  wider 
  range 
  of 
  conditions. 
  By 
  the 
  use 
  of 
  curved 
  lifting-surfaces 
  

   the 
  average 
  altitudes 
  can 
  be 
  increased 
  to 
  about 
  64°, 
  or 
  nearly 
  S° 
  higher 
  than 
  

   that 
  attained 
  by 
  kites 
  with 
  flat 
  surfaces, 
  and 
  curved-surfaced 
  kites 
  will 
  main- 
  

   tain 
  a 
  higher 
  altitude 
  in 
  strong 
  winds. 
  

  

  A 
  new 
  method 
  of 
  building 
  kites 
  was 
  described 
  whereby 
  the 
  time 
  and 
  cost 
  of 
  

   constructing 
  aerological 
  kites 
  is 
  less 
  than 
  one 
  half 
  that 
  required 
  to 
  produce 
  

   kites 
  of 
  the 
  usual 
  patterns 
  and 
  the 
  processes 
  of 
  adjustment 
  and 
  repairing 
  

   greatly 
  simplified. 
  

  

  With 
  kites 
  and 
  accessories 
  described 
  in 
  which 
  harmful 
  resistances 
  have 
  been 
  

   reduced 
  to 
  the 
  lowest 
  point 
  easily 
  attainable, 
  ascensions 
  may 
  be 
  extended 
  to 
  

   a 
  greater 
  average 
  height 
  than 
  has 
  been 
  possible 
  heretofore 
  with 
  less 
  labor 
  and 
  

  

  